In an Ethernet system, two Ethernet devices are directly connected via a cable. A link between the two Ethernet devices is a conventional Ethernet link and a working distance between the two Ethernet devices is within 100 meters. In order to realize long-reach Ethernet communication longer than 100 meters, a long-reach Ethernet device is proposed at present. The long-reach Ethernet device adopts an advanced coding method to decrease a code rate of Ethernet data, so as to extend the working distance from 100 meters to 500 meters or even to a longer distance. A link between two long-reach Ethernet devices is a long-reach Ethernet link for bearing long-reach Ethernet data. It is required in the long-reach Ethernet communication that two communication ends are both long-reach Ethernet devices and the long-reach Ethernet devices are connected with each other directly via a cable. However, a large number of existing Ethernet devices are constructed by a conventional Ethernet technology. Therefore, if one of two Ethernet devices needing long-reach communication is a conventional Ethernet device, the communication between the two Ethernet devices cannot be performed normally.
At present, a Powered over Ethernet (POE) technology which is defined in IEEE802.3af-2003 published by the IEEE standard committee also requires that two communication ends have the same type and are directly connected with each other. The POE technology provides power to data terminal devices via a cable having four twisted pairs. FIG. 1 to FIG. 3 show three kinds of POE systems defined in IEEE802.3af-2003.
FIG. 1 is a schematic diagram illustrating the structure of a POE system in an Endpoint Power Sourcing Equipment (PSE) mode A in the prior art. As shown in FIG. 1, the POE system includes a PSE unit 11 and a Powered Device (PD) unit 31. The PSE unit 11 is configured in a network switch device 10 acting as a power sourcing end. The network switch device 10 may be a hub, a switch or a router. The PD unit 31 is configured in a powered terminal 30 acting as a powered end. The powered terminal 30 may be an Ethernet data terminal such as an IP telephone, a wireless local network Access Point (AP) or a network video camera. The network switch device 10 and the powered terminal 30 are directly connected via a cable 20. Wires 1/2 (“1/2” represents a wire 1 and a wire 2), wires 3/6, wires 4/5 and wires 7/8 in the cable 20 respectively form a twisted pair. 10 Mbps Ethernet and 100 Mbps Ethernet transmit Ethernet data respectively via one or two twisted pairs in the cable, and 1000 Mbps Ethernet transmits Ethernet data via four twisted pairs. Taking an example that the Ethernet data are transmitted via two twisted pairs, two twisted pairs formed by wires 1/2 and wires 3/6 in the cable 20 respectively act as a data pair 22, and two twisted pairs formed by wires 4/5 and wires 7/8 are unused and respectively act as a spare pair 24. Each data pair 13 in the network switch device 10 is coupled to one data pair 22 in the cable 20 via a transformer 12. Positive and negative power outputs of the PSE 11 are respectively connected with center taps of two transformers 12, so as to apply power between the two data pairs 22. The two data pairs 22 bear Ethernet data and the power at the same time, where the Ethernet data are alternate current signals, the power is a direct current signal, and thus they can be differentiated according to different frequencies. Each data pair 33 in the powered terminal 30 is coupled to one data pair 22 in the cable 20 via a transformer 32. The PD unit 31 is connected with two center taps of two transformers 32, so as to obtain the power from the two data pairs 22.
In the Endpoint PSE mode A shown in FIG. 1, the data pairs 22 bears the power. FIG. 2 shows an Endpoint PSE mode B in which the spare pairs 24 bears the power. As shown in FIG. 2, the difference between FIG. 1 and FIG. 2 lies in that, in FIG. 2, the positive and negative power outputs of the PSE unit 11 are respectively connected with the two spare pairs 24, so as to apply the power between the two spare pairs 24. Thus, the data pairs 22 are only used for transmitting the Ethernet data, and the PD unit 31 obtains the power directly from the spare pairs 24. In both FIG. 1 and FIG. 2, the PSE unit 11 is configured in the network switch device 10, and thus the modes shown in FIG. 1 and FIG. 2 are called as Endpoint PSE modes. FIG. 3 shows a Mid span mode in which the PSE unit 11 is configured in an intermediate device.
FIG. 3 is a schematic diagram illustrating the structure of a POE system in a Mid span mode in the prior art. As shown in FIG. 3, the PSE unit 11 in this system is configured in a mid-span device 40, and the direct current power outputted by the PSE unit 11 is applied between the two spare pairs 24. Thus, the PD 31 needs to obtain the power from the two spare pairs 24.
In the above three solutions, whether the data pairs or the spare pairs are used to bear the power, the device where the PSE unit 11 is located is directly connected with the device where the PD unit 31 is located via a cable. Therefore, when at least one of the device where the PSE unit 11 is located and the device where the PD unit 31 is located is a conventional Ethernet device and a working distance between them is longer than 100 meters, it is impossible to provide the power to the PD by adopting the existing POE systems.
To sum up, in the existing Ethernet systems, if at least one of two Ethernet devices is a conventional Ethernet device and the working distance between the two Ethernet devices is longer than 100 meters, the two Ethernet devices cannot exchange data normally and cannot provide power to the Ethernet by adopting the exiting POE technology.